Analyzer and method of control



April 11, 1961 F. w. KARASEK ETAL 2,979,385

ANALYZER AND METHOD OF CONTROL Filed June 15, 1956 2 Sheefs-Sheet 1 HM Q ATTORNEYS April 1961 F. w. KARASEK ETAL 2,979,385

ANALYZER AND METHOD OF CONTROL Filed June 15, 1956 2 Sheews-Sheet 2 N I I Onooocooooook FIG. 3

INVENTORS F.W. KARASEK J.G. SKINNER A 7'TORNEYS nited 1 2,979,385 ANALYZER AND METHOD OF CONTROL Francis W. Karasek, Bartlesville, kla., and John .G.

Skinner, Corvallis, 0reg., assignors to Phillips Petrolenm Company, .a corporation of Delaware Filed June 15, 1956, Ser. No. 591,621 ,4 Claims. (Cl. 23-253)- to yield phosphoric acid and calcium sulfate dihydrate, or gypsum. An important side reaction is that involving fluorine, present initially in the rock as calcium fluoride'or in a combined form as lluorapatite. The fluorine is largely converted to silicon vtetrafiuoride, hydrofium silicic acid and fiuosilicates.

,In this operation, a small and closely controlled excess of sulfuric acid is desirable. The concentration of this excess sulfuric acidis important because of its elfecton the character of the gypsum crystals. The crystals are removed by filtration and the filter cake is washedto recover additional phosphoric acid. If the excess sulfuric acid-concentration in thereactor varies beyond relatively narrow limitsflthe crystal structure of the gypsum isadversely affected, giving'rise to difficulties in filtration'and washing, with -a consequent decrease in system capacity and eflicienc-y; The excess sulfuric acid concentration is generally maintained at approximately 2.5 percent :by .weight. r i

A photometric analyzeris provided in accordance with the present invention to measure the sulfuric acid concentration. 'A colorless solution containing barium ions; -is directed through a first cell to a mixing chamber. A

2,979,385 Patented Apr. 11,1961

' 16 therein. The mixture in reactor overflows through a conduit thinto a second reactor .19 which is provided with a stirrer 20 that .is driven by a motor 21. The mix- 7 ture is again agitated Lin reactor .19 and overflows .into

an outlet conduit "23. Additional reactors in seriesmay be employed, if desired. In some applications a single reactor is all that is required. v

A sample of the material in reactor 19 is withdrawn through a conduit 24, which has a filter 22 therein, and is directed by a pump .25 to .an'analyzer 26. The samplelimit, the rate of acid addition is decreased. Converse- :ly, if themeasu'red concentration of the sulfate ions gshould "decrease 'below a second predetermined limihthe rate of .acid addition is increased. Controller 28 can be a conventional instrument which provides an output regulated air pressure, for example, proportioned to an 3-1 which have radiation transparent windows.

inputelcctrical signal; Obviously, the rate of phosphate rock :could be controlled in response to analyzer 25.

"However, control of the acid is more easily accomplished.

Analyzer '26 'is illustrated in detail in Figure 2. This analyzer comprises first and second sample cells 3i; and A first beam of radiation is directed from a lamp 32; by a collimating lens :33 through cell Stlto impinge upon a photo- (cell 34; A second beam of radiation from lamp 322 is directed by a second collimating lens 35 through cell 31 sample .oimaterial-from the reactor is addedto the cham- .vide a photometric analyzer to determine[the sulfate. ion 7 concentration in'a liquid sample. t I

vAnother objectis'to provide a method ofand z p-- paratus for regulating chemical reactionsin' response to an. analysis of .a sample from the reactor.

Another object is to provide apparatusafo'r controlling in the production .pf-phosphoric acid.

the:- -rate of addition of sulfuric acid to phosphate rock Other objects, advantages and featuresofthe ig'rven-l tion should becomeapparent from-the followingdetailed Y description, taken in conjunction with the accompanying drawingi-nwhich: j I 1 '-Figure 1 is a schematic, representation of a-;control I system for apparatus used in the production of phos- I horic acid; Fi r r metric analyzer.cfihis'invention; and I W a; schematicrepresentation of the plioto- 1 to impinge *upon a second, photocell 36. Corresponding first terminals of photocells-34 and 36 are connected to one another and to' the contactor of a potentiometer Thesecond terminal of photocell 344s connected through a potentiometer '38 and a variable'resistor 35 to the first end terminal of potentiometer 37. The second terminal of photocell 36 is connected through a potentiorneter 4t) and aivariable resistor 41 to the second end terminal of potentiometer 37. Variable'resistors 39 and a l]; are mechanically connected 'to one another so that an increase in resistance of one results in a correspond- .ingjncrease in the resistance of the other; 'lhis permits the sensitivity of the bridge circuit to be varied. The contactorsof potentiometers 38 and 40 are connected .,to the respective input terminals- 0f a servo amplifier 4'2.

The output signal from amplifierdz energizes a reversible motor 43. The drive shaft of motor 43 is connected I of Figure "1. j r

to the contactor-of potentiometer 37. y

- The drive shaft of motor 43 isalso'connected to the .contactor of a telemetering potentiometer tentiometer 45. The contactor and one end terminal of potentiometer 45- are connected to respective 'output termh rials 47 and 48- whichin turn are connected to controller The outlet of a liquid storagetank Sti ls connected bymeans of a conduit 51", having a pump 54 therein, ,to

*the inlet of an'overflow tank52. '.An overflow conduit 55 returnsf'to tank .50. Liquid at a constant pressure is I -direct ltf sm aa c SZ' w sh asn u fi, h in a Y I A voltage sourcedfi ris connected across the end terminals of po-.

metering pump 57 therein, to the inlet of cell 30. This liquid flows from cell 30 to a container 53. From container 53, liquid flows by gravity through cell 31 to an overflow drain 58.

Tank 50 contains a 0.4 weight percent aqueous solution of barium chloride, for example. This concentration can vary considerably, and other solutions which contain barium ions can be so employed. This colorless solution is directed through cell 30. A sample from conduit 24 is added to container 53 in the manner described hereinafter in detail. The sulfate ions in the sample combine with the barium ions to form barium sulfate, a white precipitate. The amount of precipitate formed is a function of the concentration of the sulfate ions in the sample stream removed from vessel 19. The

resulting material is directed through sample cell 31.

The amount of radiation transmitted through cell 31 is thus less than the radiation transmitted through cell 30 so that photocell 36 generates less current than does photocell 34.

The output currents from photocells 34 and 36 are connected in opposition to one another across the illustrated bridge network. The bridge initially is balanced -under reference conditions by moving the contactors of potentiometers 38 and 40 in unison. A balanced condition is obtained when the potentials at the contactors of the two potentiometers are equal. Any change. in the relative amounts of light transmitted through the two sample cells changes the relative currents generated by the two photocells so that the potentials at the contactors of potentiometers 38 and 40 are no longer equal. This results in a direct current signal being applied to the input terminals of amplifier 42. The polarity of this signal depends upon the relative light transmissions 9 terminals 90 and 86. Terminal 90 is connected to the through the two sample cells. This direct current signal is converted into a corresponding alternating current signal which is amplified and applied to motor 43. Motor 43 rotates in a direction to move the contactor of potentiometer 37 until the bridge circuit is again balanced, as indicated by the potentials at the contactor of potentiometers 30 and 40 being equal. Amplifier 42 and motor '43 can be any known type of equipment, such as of the form described in Electronic Control Handbook, Batcher and Moulick, Caldwell-Clements, Inc., New York, 1946, page 298, for example.

One of the problems encountered in analyzers of this type is that of obtaining reproducible stable colloidal This is due to the fact that the turbidity 'trolling the rate of addition of the sample stream to container 53. A conduit 60, having a needle valve 61 'therein, communicates at oneend with the junction between sample conduits 2.4- and 27. The second end of conduit 60 terminates at a region above container 53 so that a portion of the sample stream circulated'through conduits 24 and 27 can be dropped into'c'ontainer 53.

Needle valve 61 is adjusted so that the stream falls into f container 53 as individual droplets. A funnel 62 normal 'ly is retained beneath conduit. 60 by means of aspring The droplets falling intoiunnel 62 are removed from the systemthrouglr a drain conduit 64, A solenoid '55 is mounted adjacent funnel62 so that the funnel is displaced against the force of spring 63 when the sole hold is energized. This permits the dropletslfrom con-- duit 60 to fall into container 53.. Container 53 is provided with a magnetically actuated stirrer 66 which provides mixing of the barium and sulfate ions.

Apparatus is provided to count the rate at which the droplets fall from conduit 60. A beam of radiation from a lamp 70 is directed by lens 71 through an aperture in a plate 72 so as to intersect the falling droplets.

This beam of radiation impinges upon a photoelectric tube 73. Each falling droplet momentarily blocks the light beam. The cathode of tube 73 is connected to ground, and the anode thereof is connected through a resistor 74 to a positive potential terminal 75. The anode of tube 73 is also connected through a capacitor 76 to the control grid of a triode 77. The control grid of triode 77 is connected to ground through a resistor 78.

5 The cathode of triode 77 is connected to ground through a resistor 79 which is shunted by a capacitor 80. The anode of triode 77 is connected to terminal 75 through the coil of a relay 81.

Each time the radiation beam is blocked by a falling droplet, the conduction through tube 73 is momentarily extinguished. This results in the potential at the anode of tube 73 increasing rapidly. The resulting positive pulse is applied through capacitor 76 to the control grid of triode 77. This pulse causes tube 77 to conduct momentarily to energize the coil of relay 81.

The apparatus employed to control needle valve 61 is illustrated in Figure 3. Needle valve 61 is adjusted by rotation of a reversible two-phase servo motor 83. The control circuit of Figure 3 is energized from a source of alternating current 84 which has output termifirst terminal of a coil 92 which energizes a stepping switch 93. The second terminal of coil 92 is connected to a first switch arm 94a of the stepping switch. Switch arm 94a is adapted to engage a first bank of contacts 20a in sequence when coil 92 is energized. Contacts 1a, 2a 15a are connected to one another and to terminal 86 through a switch 95 which is closed each time relay coil 81 is energized. The second terminal of coil 92 is also connected through an interrupter switch 9.6 to a second switch arm 940 of the stepping switch.

Switcharm 940 is adapted to engage contacts 10, 2c

20c in seqence. Contacts 160, 170,180, and 190 are connected to one another and to terminal 86. Contact 20c is connected through switches 100 and 101 to terminal 86; Stepping switch 93 is provided with a third switch arm 94b which is adapted to engage contactslb, 2b 20b in sequence. Contacts 1b, 2b 15b are connected to one another andto terminal'86. Switch arm 94b is connected to terminal '90 through the coil of. arelay 102. A capacitor 103 is connected in parallel with the coil of relay 102.

The coil of a relay 104 is connected between terminals and 86 through switch 101. A capacitor 105 is connected in parallel with the coil of relay 104. 'Motor 83 60 is provided with first andsecond windings 106 and 107 which are mounted at right angles to one another. Corresponding first terminals of windings 106 and 107 are connected to oneanother and to terminal 85. A capacitor 108 is connected between the second end terminals of 65 windings 106 and 107. ,The second terminal of windingflltie is connected through switches. 109 and 110 to terminal 86. The second terminal of winding 107 is connected through switches 111 and 112 'to terminal 86. Switch 109 is opened and switch 112 is closed when relay 70102 is energized. Switch 111 is opened and switch 110 75 so'urce'84. A third cam a is rotated by motor 114 to close a switch 115. Switch 115 is connected in circuit with a voltage source 116 and solenoid 65. It is normally desired that only about one out of every thirty drops from conduit 60 falls into container 53. Cam 115a is set so that switch 115 is closed momentarily to permit funnel 62 to be displaced. This can occur once every minute, for example. Cam 100a is set to close switch 100 momentarily at the beginning of each calibration cycle. Cam 101a closes switch 101 at the beginning of each calibration cycle and keeps the switch closed a predetermined time interval, which can be one-half minute, for example.

The calibration cycle begins by cam 100a closing switch 100 momentarily. Switch 101 is closed almost immediately thereafter to energize relay 104. At the same time, the stepping switch is advanced one position because a circuit is completed through coil 92 by means of switch arm 94c and contact 20c. This moves the three switch arms to the first contacts. Relay 102 is energized through switch arm 94b and contact 1b. Thus, relays 102 and 104 are energized almost simultaneously at the beginning of the cycle. The stepping switch is then energized to move the switch arms to the next contacts each time relay 81 is energized by a droplet from conduit 60 interrupting the radiation beam. At the end of the one-half minute period, switch 101 is opened by cam 101a. This deenergizes relay 104. Motor 83 is then connected across current source 84 so as to be rotated in a first direction if relay 102 is still energized. This rotation of motor 83 is in a direction so as to increase the opening in needle valve 61 to increase the dropping rate. Motor 83 thus continues to rotate until the switch arms move into engagement with the 16th contacts. At this time, relay 102 is deenergized so that motor 83 is no longer connected to current source 84. The arms of the stepping switch are rapidly returned to the 20th contacts by the circuit completed through contacts 16c, 17c, 18c, and 190.

If the dropping rate should be such that the arms of the stepping switch reach the 16th contacts before switch 101 is opened, relay 102 becomes deenergized while relay 104 remains energized. This connects motor 83 across current source 84 in the opposite manner so that the motor is rotated in a second direction. This motor rotation tends to close needle valve 61 and decrease the dropping rate. Needle valve 61 thus tends to be positioned so that 15 droplets fall from conduit 60 during the period, one-half minute, that switch 101 is closed by cam 101a.

The particular number of droplets in a given time interval obviously depends upon the size of needle valve 61 and the desired rate of sample addition to container 53. The number of contacts employed on the stepping switches and the length of timing cycle obviously can be varied to accommodate difierent desired rates. This rate obvious-1y depends on the reagent concentration and circulation rate and the sample concentration. Excellent results were obtained with the reagent previously described circulated at a rate of 15 cc. per minute and the sample dropped at the rate of 30 drops per minute, or 2 cc. per hour.

In view of the foregoing description, it should be apparent that there is provided in accordance with this invention an improved photometric type analyzer and a control system based thereon. While the invention has been described in conjunction with a present preferred embodiment, it obviously is not limited thereto.

What is claimed is:

1. Apparatus for use in the production of phosphoric acid and for maintaining the sulfate ion concentration thereof within a predetermined range, comprising: a first mixing vessel; means to add phosphate rock to said vessel; means to add sulfuric acid to said vessel; means to withdraw a sample stream from said vessel; analyzer means to measure the concentration of sulfate ions in said removed sample stream, said analyzer means comprising first and second sample cells, means to direct first and second radiation beams through said first and second cells, respectively, a second mixing vessel, means to direct a reagent through said first cell into said second vessel, said reagent being a reagent which will react with said sulfate ions in said sample stream and change the light transmission properties thereof, means to add at least a portion of said removed sample stream to said second vessel, means to direct the resulting mixture of said reagent and said portion of said sample stream from said second vessel through said second cell, and comparison means to compare the radiation beams transmitted through said first and second cells; means responsive to said comparison means to control the relative rates of addition of said sulfuric acid and said phosphate rock to said first mixing vessel; and means for recovering phosphoric acid product having a predetermined sulfate ion concentration.

2. Apparatus according to claim 1 wherein said reagent is a solution containing barium ions.

3. Apparatus according to claim 1 wherein said means to control comprises means to vary the rate of addition of said sulfuric acid to said first mixing vessel.

4. Apparatus according to claim 1 wherein said reagent comprises an aqueous colorless solution of a barium salt having a minor amount of gelatin therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,013,970 Moore Sept. 10, 1935 2,019,871 Petingill Nov. 5, 1935 2,044,164 Gulliksen June 16, 1936 2,362,278 Jones Nov. 7, 1944 2,417,877 Lewis Mar. 25, 1947 2,462,995 Ritzman Mar. 1, 1949 2,504,544 Legal et al. Apr. 18, 1950 2,504,545 Waring et al Apr. 18, 1950 2,611,681 Bellinger Sept. 23, 1952 2,656,845 Lindsay Oct. 27, 1953 2,694,335 Albright et al. Nov. 16, 1954 2,741,544 Chaikin et al. Apr. 10, 1956 

1. APPARATUS FOR USE IN THE PRODUCTION OF PHOSPHORIC ACID AND FOR MAINTAINING THE SULFATE ION CONCENRTATION THEREOF WITHIN A PREDETERMINED RANGE, COMPRISING: A FIRST MIXING VESSEL; MEANS TO ADD PHOSPHATE ROCK TO SAID VESSEL; MEANS TO ADD SULFURIC ACID TO SAID VESSEL; MEANS TO WITHDRAW A SAMPLE STREAM FROM SAID VESSEL; ANALYZER MEANS TO MEASURE THE CONCENTRATION OF SULFATE IONS IN SAID REMOVED SAMPLE STREAM, SAID ANALYZER MEANS COMPRISING FIRST AND SECOND SAMPLE CELLS, MEANS TO DIRECT FIRST AND SECOND RADIATION BEAMS THROUGH SAID FIRST AND SECOND CELLS, RESPECTIVELY, A SECOND MIXING VESSEL, MEANS TO DIRECT A REAGENT THROUGH SAID FIRST CELL INTO SAID SECOND VESSEL, SAID REAGENT BEING A REGENT WHICH WILL REACT WITH SAID SULFATE IONS IN SAID SAMPLE STREAM AND CHANGE THE LIGHT TRANSMISSION PROPERTIES THEREOF, MEANS TO ADD AT LEAST A PORTION OF SAID REMOVED SAMPLE STREAM TO SAID SECOND VESSEL, MEANS TO DIRECT THE RESULTING MIXTURE OF SAID REAGENT AND SAID PORTION OF SAID SAMPLE STREAM FROM SAID SECOND VESSEL THROUGH SAID SECOND CELL, AND COMPARISON MEANS TO COMPARE THE RADIATION BEAMS TRANSMITTED THROUGH SAID FIRST AND SECOND CELLS; MEANS RESPONSIVE TO SAID COMPARISON MEANS TO CONTROL THE RELATIVE RATES OF ADDITION OF SAID SULFURIC ACID AND SAID PHOSPHATE ROCK TO SAID FIRST MIXING VESSEL; AND MEANS FOR RECOVERING PHOSPHORIC ACID PRODUCT HAVING A PREDETERMINED SULFATE ION CONCENTRATION. 